I am seriously curious - why not backup some sys data with Ti-Backup?
I wanna keep all my wifi passwords and mail accounts and sense desktops - serious ball ache to redo all of this stuff - whats the problem with restoring a ti-backup of these items?
Thanks in advance

Thankyou for the hard work, without dev's I would be stuck in the land of gingerbread still!

Restoring system data can cause serious issues. The data belong to apps that are (or might be) exchanged by the rom update. So those data may not be totally compatible with the updated apps and therefore produce unpredictable results.
If you want to keep wifi settings and mail accounts, you should consider using ROM-Cleaner (Link in 2nd Post). It can backup your settings before flashing and reinsert them automatically (NOT restoring, but simulating new entry) after flashing. Also Sense settings as far as that is possible. Widgets are not totally restorable, neither with TB nor with any other tool.

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